It wasn't the government that killed the Syrian rebel commander Abu Jameel. It was the fight for his loot. The motive for his murder lay in a great warehouse in Aleppo which his unit had captured a week before. The building had been full of rolled steel, which was seized by the fighters as spoils of war.

But squabbling developed over who would take the greater share of the loot and a feud developed between commanders. Threats and counter-threats ensued over the following days.

Abu Jameel survived one assassination attempt when his car was fired on. A few days later his enemies attacked again, and this time they were successful. His bullet-riddled body was found, handcuffed, in an alley in the town of al-Bab.

Captain Hussam, of the Aleppo military council, said: "If he had died fighting I would say it was fine, he was a rebel and a mujahid and this is what he had set out to do. But to be killed because of a feud over loot is a disaster for the revolution.

"It is extremely sad. There is not one government institution or warehouse left standing in Aleppo. Everything has been looted. Everything is gone."

Captured government vehicles and weapons have been crucial to the rebels since the start of the conflict, but according to Hussam and other commanders, and fighters interviewed by the Guardian over a fortnight in northern Syria, a new phase has been reached in the war. Looting has become a way of life.

"Spoils" have now become the main drive for many units as battalion commanders seek to increase their power.

The problem is particularly pronounced in Aleppo, according to Abu Ismael, a young lieutenant from a wealthy family, who ran a successful business before joining the fight against Bashar al-Assad.

Many of the battalions that entered the city in the summer of this year came from the countryside, he said. They were poor peasants who carried with them centuries-old grudges towards the wealthier Aleppans.

There was also a lingering feeling that the city – where businesses had been exploiting cheap peasant labour for several decades – had not risen up quickly enough against the Assads. "The rebels wanted to take revenge on the people of Aleppo because they felt that we had betrayed them, but they forgot that most of the people of Aleppo are merchants and traders and a merchant will pay money to get rid of his problem," Abu Ismael said. "Even as the rest of Syria was gripped by revolution, the Aleppans said, why should we destroy our business and waste our money?"

When the rebels entered the city and started looting the factories, a source of money dried up.

"In the first month and a half the rebels were really a united revolutionary group," Abu Ismael said. "But now they are different. There are those who are here only to loot and make money, and some still fight." Did Abu Ismael's unit loot? "Of course. How do you think we feed the men? Where do you think we get all our sugar, for example?"

In the chaotic economics of the war, everything has become a commodity. Abu Ismael's unit, for example, took a supply of diesel from a school compound, and every day his unit exchanges a few jerrycans of the precious liquid for bread.

Because Abu Ismael has a supply of food and fuel his battalion is more desirable than others in the sector. Commanders who are unable to feed their men tend to lose them; they desert and join other groups.

Bullets are equally important. When military installations and warehouses are looted the battalion that captures ammunition grows by cannibalising smaller, less well-equipped units that have no bullets to hand.

In a dark apartment in the Salahuddin neighbourhood of Aleppo we sat with a group of commanders who were discussing the formation of a new brigade that would bring their various battalions together. They soon turned to the topic of loot.

One of the commanders present had led an operation into the predominantly Kurdish neighbourhood of Ashrafiya in Aleppo, but according to several fighters who were there the action failed when the army counterattacked because the rebel support units that were supposed to reinforce the front instead turned their attention to looting.

"I want to know exactly what you took that day," the commander of a small unit told the leader of the assault. The commander opened a notebook to write, while another man held a flashlight above his head. "As long as one fights while the others are busy collecting loot we can't advance," he said. "The loot has to be divided equally."

The leader started to list the luxury cars and the weapons his units had found and taken, while the other commander wrote them down in the notebook. Some of the cars would be sold back to the owners – if they paid out a hefty ransom.

Outside sponsors

The war in Aleppo is not only funded by what can be appropriated by the various units, but also by the patronage that they can attract from sponsors outside Syria, a factor which has also contributed to the myriad forming and re-forming of units, all of which control individual fiefdoms in the city.

All of this has fuelled rivalries and ever-shifting allegiances, factors that have undermined the struggle to defeat the forces of the Syrian president.

Fighting units often exist only because of their sponsors. If a sponsor loses interest a battalion is dissolved and the men join another, better-funded battalion. Battalions are often named after historical Arab or Ottoman figures in order to help lure money from the Gulf kingdoms or from Turkey.

One Friday afternoon after prayers a group of the most senior commanders fighting in Aleppo, 32 in all, gathered in part of a sprawling former government compound, the building's once polished marble floors now covered with puddles of water, its walls blackened by soot. Sitting in low leather chairs around a large table, many of the men carried the scars of two years of fighting – missing eyes, lame arms, crippled legs.

The meeting was chaired by Abdulkader al-Saleh, a leader of the Tawheed brigade, one of the biggest and best equipped rebel battalions in Syria.

First on the agenda was the task of reintroducing the men to each other, as many had switched battalions since their last meeting in the endless game of musical chairs of the Syrian revolution.

A who's who of the revolution followed, each commander stating his name and his unit. Some battalions were huge, with hundreds of men, artillery pieces and tanks. Others consisted of fewer than 50 fighters.

"Haji, I thought you were with Halab al-Shaba'a brigade," Haji Marea said to one of the men. "No, we have reformed. We are a new battalion," the man said.

"Brothers, we have a grave situation ahead of us," interjected Abdul-Jabbar Akidi, a defected colonel who leads the military council of Aleppo. Formed to channel supplies to the rebels, the council was supposed to be the overarching command structure for the Free Syrian Army in Aleppo. Instead, it soon became one more faction among many competing for influence.

"The battle has stagnated here," he said. "There has been no real progress on the fronts and that has affected our sponsors, who haven't been sending us ammunition.

"Even the people are fed up with us. We were liberators, but now they denounce us and demonstrate against us. We have to unite and form an operations room for all the battalions."

Soon, however, the conversation took a familiar turn, moving on to complaints about units keeping equipment to themselves.

A short, clean-shaven commander in a leather jacket spoke up: "The problem is that some battalions have artillery and tanks and they are keeping them for themselves and not participating in the attack. Bring me the pieces that were captured from the base of the 46th brigade [a government unit] and I will take over the secret police buildings in Aleppo without having to send my men to die in front of government snipers."

The second item on the agenda concerned the formation of a revolutionary police force.

As the revolution in Aleppo stagnated and the rebel commanders settled in to rule their "liberated" neighbourhoods, each battalion had started forming its own revolutionary security service, or Amn al-Thawra, manning checkpoints and detaining people, which had led to a spike in kidnapping.

The commanders put forward proposals for how they could create a single disciplined security force.

One moustachioed former colonel in a brown suit began reading what sounded like a Ba'ath party manifesto: "I call for the formation of a secret bureau of revolutionary military security service," he said.

Many of the men in the room had been detained and tortured by Assad's security services and sank into their chairs as the former colonel spoke.

"We fought against the regime because of these secret security forces," said a man with a thick rural accent.

Another battalion commander with a soft voice and a neat blue turban began to speak. "I call for the formation of a small unit of our brothers, the religious students," he said. "Their job would be to advise the people before the need to use force."

He added: "They will be armed with their wisdom and religious teaching and it should be called the committee of ruling with virtue and the prevention of vice. It will be the first step in preparing the people for an Islamic society."

At this, a young fighter shouted from one end of the room: "The problem is not with the people. The problem is us! We have battalions sitting in liberated areas who man checkpoints and detain people. They say this person is a shabiha [a government militiaman] and take his car, or that man was a Ba'athist, take his house.

"They have become worse than the regime. Tell me why those men are in the city, in liberated areas, why are they not fighting at the frontline?"

As the room choked with the smoke of cigarettes, the commanders agreed to form one unified security force. Yet weeks later, there would be little evidence of that force.

Abandoned posts

There were many further stories of looting heard during the our time in Aleppo. A pharmacist who had volunteered as a medic in one of the rebel field hospitals explained why he was running short of penicillin.

The rebels had taken over the warehouse of a leading pharmaceutical company and then had resold the stock back to the owners, shipping all the drugs back into government-held territory, he claimed.

He added: "I went to the warehouse to tell them they had no right to the medicine and that it should be given to the people and not re-sold. They detained me and said they would break both my legs if I ever went back."

In Saif al-Dawla district a commander who was furnishing a new headquarters for his newly formed battalion walked into a school compound with a few of his men.

A group of civilians stood watching in the late afternoon as the men trawled through the school. Burned and torn pictures of Assad lay on the floor. Desks and chairs were upturned and broken, and plastic flowers and students' projects were strewn around.

The men ferried some of the tables, sofas and chairs outside the school and piled them up at the street corner. Computers and monitors followed.

A fighter registered the loot in a big notebook. "We are keeping it safe in a warehouse," he said.

Later in the week I saw the school's sofas and computers sitting comfortably in the commander's new apartment.

On the frontlines of the Ameriya neighbourhood, south of Aleppo, we met Abara and his men.

Abara is young and short, in his early 20s, with fair hair and few pimples scattered on his face. He had defected from the army a year earlier. We had first met three months earlier when he was leading his men through the alleyways of Salahuddin, and many of those fighters had been killed or maimed since then.

He was now sitting with the survivors on a cold concrete floor in an abandoned building a block away from government troops. Between the men was a jar of greasy-looking green olives, a bag of bread, a plate of olive oil and some thyme. "It's much worse now," Abara said of the war. "Now it's copper and wheat that commanders are after instead of liberating the city."

He added: "The problem when people stop fighting – I liberate an area, I need resources and ammunition, so I start looting government properties. When this has finished I turn to looting other properties and I become a thief."

The physical ground that, at the moment, lay between him and the government line consisted of a series of shattered buildings where snipers from both sides appeared to shoot at almost anything that moved.

"When the army attacked us last week the unit that was here abandoned their posts and withdrew," he said.

Now, he said, in order to regain the lost territory he would have to fight house to house. "Why should I, when the rest are looting?"

He added wearily: "One day when the war against Bashar is over, another war will start against the looters and thieves."